WO2018109378A1

WO2018109378A1 - Mixture for treating mercury-polluted water, device for treating mercury-polluted water using such a mixture and method for treating mercury-polluted water by means of such a device

Info

Publication number: WO2018109378A1
Application number: PCT/FR2017/053543
Authority: WO
Inventors: Boris DEVIC-BASAGET; Amandine ROMANO; Jean-Yves RICHARD
Original assignee: Suez Rr Iws Remediation France
Priority date: 2016-12-13
Filing date: 2017-12-13
Publication date: 2018-06-21
Also published as: ES2957697T3; EP3555004B1; FR3059996A1; MA48598A; FR3059996B1; EP3555004A1

Abstract

The present application relates to a use of a mixture (6) including iron and a chemically inert granular support for treating mercury-polluted water. It also relates to a device for treating mercury-polluted water containing a filtering reagent (5, 6, 7) which includes the mixture (6) of iron and the chemically inert granular support. The invention also relates to a method for treating mercury-polluted water by such a device, including a step of injecting a volume of water into an enclosure (1) of the device; a step of the water volume transiting in contact with the filtering reagent (5, 6, 7); a step of precipitating the mercury, with the iron of the iron/granular support mixture (6), including a step of reducing the mercury and a step of forming microdroplets of mercury; and a step of extracting the volume of water from the device.

Description

Mercury-contaminated water treatment mixture, mercury-contaminated water treatment device using such a mixture and method for treating mercury-polluted water by means of such a device The present application relates to a treatment mixture of water polluted with mercury.

It also relates to a mercury polluted water treatment device using such a mixture.

It also relates to a method of treating water polluted with mercury by means of such a device.

A "water" is understood here in a broad sense, any industrial effluent, any groundwater, canal, river, river, torrent, lake or sea, ocean etc., natural or artificial.

In fact, it is possible that water in nature is polluted by mercury, although in general the mercury impacts come from industrial activity such as old salt electrolysis plants, mining or laboratories.

There are mercury-contaminated water treatment devices that use reducing agents.

The most used principle consists of two steps. A reduction step that includes a step of adding a reducing agent in water polluted with dissolved ionic mercury or ionic elemental mercury, finely divided or colloidal, which causes the precipitation of mercury. An extraction step in which the mercury is extracted either by filtration or by distillation.

The documents GB1368966, BE818422 or US3857704 deal with the use of iron, mainly in the form of ferrous sulphate or iron or steel chips, for the depollution of mercurial waters. In this case, the iron is added directly to the water in an infinitely mixed medium to carry out the reduction step. This step requires pH regulation which complicates the process. There are also patents which relate to the reduction of mercury by a sulfur compound such as Na2S (CN102372377) or hydrosulfite (GB1350703), which allows the formation of insoluble mercury sulfide (HgS). Once the mercury insolubilized, it is extracted from the water by distillation (which is for example described by the documents US3857704 or GB1368966) or filtration (BE818422, GB1339261, GB1350703, US4098697, CN102372377).

The recovery of insolubilized mercury on filter is also widely described in the literature. The filter media are of various forms ranging from simple physical filtration with the use of sand (CN102372377 for example) or activated carbon (US6165366) for distillation which consists in bubbling an inert gas in water to volatilize the mercury. then to treat mercurial vapors.

However, water usually contains dissolved oxygen and other compounds (nitrates, sulphates, etc.) capable of oxidizing iron. Depending on the type of oxidation (Fe (0) to Fe (II), or Fe (II) to Fe (III)) which causes swelling of the iron particles, when the iron is used as a filter medium, a setting in mass fragments of iron between them and / or a formation of precipitates of oxides and hydroxides of iron occurs causing, in both cases, a rapid clogging of iron.

The systems known from the prior art are therefore complex and / or unsatisfactory; the associated processes include many successive steps, also complex, and are intended to recover the mercury contained in the water.

At least one of the objectives of the present application is thus to solve, at least in part, the aforementioned drawbacks, leading in addition to other advantages.

For this purpose, is proposed, in a first aspect, a mercury polluted water treatment device comprising: an enclosure containing a filtration reagent, a water inlet to be treated in the chamber upstream of the filtration reagent and a treated water outlet of the enclosure downstream of the filtration reagent, characterized in that the filtration reagent comprises a mixture of iron and a chemically inert granular support, that is to say a carrier of chemically inert particles.

The chemically inert granular support comprises, for example, sand and / or siliceous gravel, silica beads, glass beads, and possibly even certain plastics.

In a preferred embodiment, the chemically inert granular support comprises sand, especially siliceous sand which is also particularly economical.

Such a device thus makes it possible to combine the reduction and the retention of mercury, in a single, simple filtration device, while preserving the effectiveness of the treatment. Such a device thus allows the direct filtration of water polluted with mercury on a granular reagent.

The latter, composed mainly of a mixture of iron and an inert granular carrier, for example and economically siliceous sand, allows both the reduction of elemental forms of mercury and their trapping in the filter.

Mercurial waters pass through the permeable mixture, and the soluble forms of mercury are reduced and insolubilized upon contact with iron.

The reduced mercury remains trapped in the mixture which progressively charges with mercury until saturation and elimination, i.e. it is simply possible to change at least the mixture when saturated.

In such a device, the granular support to ensure, when the proportion of iron and limited in the mixture, a distance between each grain of iron, limiting the direct contact iron / iron and consequently the clogging of the reagent.

The granulometry of the granular support is chosen according to that of the iron used so as to respect the laws of non-segregation of iron by gravity and / or by backwashing.

In an exemplary embodiment, to better help to avoid the segregation or the gravitational separation of the iron in the inert support, a ratio N = D15 d85 - with D15 corresponding to the diameter passing from the granular support to 15% by weight and d85 to the diameter passing iron at 85% by weight - is equal to or less than 1 1; preferably, N is between about 3 and about 5. Thus, the iron can not separate from the mixture by erosion or gravity regardless of the filtration rate that passes through the filtration reagent.

Iron is used for its reducing power. This reducing agent may be indifferently iron or an alloy containing iron such as steel (not stainless) or cast iron.

In other words, "iron" here means zero valent iron, that is to say metallic, which has a high reducing power, and not oxides, hydroxides, or iron oxyhydroxides, for example.

As a reducer, the reactivity of iron is directly proportional to its developed surface.

Thus different types of iron can be used: the iron is for example in the form of shot, and / or powder and / or chip, and / or any other fractional form allowing the penetration of water. Each shape develops a contact surface and a different permeability. The type of iron is further selected to not bring additional pollution downstream of the filter reagent, especially metal pollution as could zinc, for example.

In a preferred embodiment, the mixture comprises between about 1% and about 50% by weight of iron, preferably between about 1% and about 25% by weight, and even more preferably between about 5% and about 20% by weight. . Such proportions make it possible to limit clogging of the mixture (the iron grains by oxidizing swell and weld together). In addition, the life of the mixture depends in particular on the proportion of iron: to some extent, the more iron, the longer the life is long for the same grain size.

According to an interesting embodiment, additives may be added to the iron-granular support mixture. That is, for example, the filtration reagent may further comprise at least one additive. For example, the filtration reagent comprises at least one additive between 0% and about 5% by weight relative to the total mass of the filtration reagent, in order to optimize the treatment and / or to influence the scope of the treatment. pollution case mercury, that is to say of mixed pollution or co-pollution. In case of several additives, the set of additives is preferably less than about 5% by weight. In other words, the filtration reagent comprises at least about 95% by weight of the granular iron-carrier mixture.

For example, the at least one additive comprises elemental sulfur, which allows the formation of mercuric sulphide (HgS) and thus makes it possible to chemically stabilize the reduced mercury.

And / or for example, the at least one additive comprises at least one specific ion exchange resin for capturing certain metal pollution such as hexavalent chromium, a recurrent pollutant of groundwater. Such a resin is for example a resin whose functional group is of quaternary ammonium type.

And / or for example, the at least one additive comprises activated carbon, to capture organic pollution.

In an exemplary implementation, the at least one additive is mixed into the mass of the iron-granular support mixture.

In another implementation example, the at least one additive constitutes at least one independent layer, implanted upstream and / or downstream of the iron-granular support mixture.

According to an interesting example, the filtration reagent may comprise several layers configured to be successively traversed by the water to be treated.

For example, if the water to be treated contains a lot of oxidizing elements (for example O2, NO3, SO4 or other), the mercury-treating granular iron-support mixture is preferably preceded by a prefiltration layer having a permeability to less than ten times that of the iron-granular support mixture, that is to say having a larger particle size, for example having iron granules of 2 mm mixed in sand at 1-2 mm, and enriched with iron by relative to the granular iron-support mixture, so as to eliminate a maximum of oxygen, but with an iron content remaining less than 50% by mass. The iron content of this pre-filtration layer is, for example, between about 20% and about 40% by weight. mass. This layer, for example, has the role of consuming most of the oxidants present in the water to be treated and thus of protecting the granular iron-support mixture, which is dedicated to mercury. This pre-filtration layer also reduces the risk of clogging of the filtration reagent.

In other words, the filtration reagent may comprise, for example, a prefiltration layer upstream of at least the granular iron-support mixture, the prefiltration layer having a permeability at least ten times greater than that of the iron-support mixture. granular material and / or an iron content for example of between about 20% and about 40% by weight.

Also provided in another aspect is a treatment mixture of mercury polluted water containing iron and a chemically inert granular carrier; which comprises for example sand and / or siliceous gravel, silica beads, glass, or possibly some plastics, preferably sand.

Such a mixture comprises for example all or part of the characteristics described above, independently of the device.

In particular, use is proposed of such a mixture comprising iron and a chemically inert granular support for treating mercury-polluted water.

In particular, such a mixture is advantageously used in a device as described above.

According to yet another aspect, a method for treating mercury-polluted water by a device comprising all or some of the features described above, comprising:

- A step of introducing a volume of water into the chamber of the device by the water inlet of the device;

A step of transit of the volume of water in contact with the filtration reagent, for a residence time equal to or less than two hours, for example between about five minutes and about twenty minutes;

A step of precipitating the mercury, with the iron of the granular iron-support mixture of the filtration reagent, comprising a mercury reduction step and a mercury microdroplet forming step; and - A step of extracting the volume of water out of the device by the water outlet of the device.

The method thus has advantages similar to those described in connection with the device.

The invention, according to an exemplary embodiment, will be better understood and its advantages will appear better on reading the detailed description which follows, given by way of indication and in no way limiting, with reference to FIG. 1 which presents a schematic cross-section of FIG. a device according to an exemplary embodiment of the invention.

The device mainly comprises an enclosure 1.

Such an enclosure, or vessel, typically has a generally cylindrical shape. It is usually made of stainless steel or high density polyethylene. The enclosure often comprises for example an access door allowing access to the enclosure and / or, for example, to fill it and / or empty filter reagent.

This is for example a tank with a capacity of a few cubic meters, for example from 1 m ³ to several cubic meters.

The device comprises a water inlet 3 to be treated in the enclosure 1, for example in the form of a channel passing through a wall of the enclosure 1 on one side of the enclosure, and an outlet 4 of treated water outside the enclosure, also for example in the form of a channel passing through the wall of the enclosure 1 on the other side of the enclosure.

Here the output 4 is opposite the inlet 3 along an axis D of the enclosure which extends generally vertically.

In particular, the inlet 3 is here formed at the bottom of the enclosure 1 and the outlet 4 is formed at the top of the enclosure 1 so that the water enters at a base of the enclosure 1 and then traverses vertically up to at the outlet 4, according to an upward flow. According to another embodiment not shown, it could be otherwise so that the flow would then downward.

The enclosure 1 is also here equipped with a grid 2. The grid 2 is for example arranged between the inlet 3 and the outlet 4, here towards the base of the enclosure, that is to say in the present embodiment closer to the inlet 3 than the outlet 4.

In addition, it is disposed along a section of the chamber 1 across its axis D. In other words, the gate is arranged to be traversed by the flow of water passing through the enclosure between the inlet 3 and the outlet 4. The grid 2 thus promotes a better homogeneity of water distribution over an entire section of the enclosure.

The device further comprises, in the chamber, a filtration reagent 5, 6, 7.

The filtration reagent is based on the grid 2.

Thus, here, the filtration reagent is disposed between the gate 2 and the outlet 4, so that the water to be treated enters the chamber through the inlet 3, passes through the gate 2, the filtration reagent 5, 6, 7, then, once treated, leaves the enclosure by exit 4.

The arrival 3 of water to be treated in the chamber is upstream of the filtration reagent 5, 6, 7 and the outlet 4 of treated water outside the enclosure is downstream of the filtration reagent.

In the present embodiment, the filtration reagent comprises several layers, in particular three layers. When the device is used, the water thus passes successively through the various filter reagent layers, in particular here a first layer 5, a second layer 6 and finally a third layer 7, in this order.

Here, the first layer 5 of the filtration reagent is for example a pre-filtration layer. Such a layer is for example configured to remove dissolved oxygen in the water.

The second layer 6 of the filtration reagent comprises for example a mixture of iron and sand configured to reduce and accumulate mercury polluting the water to be treated.

The third, and last, layer 7 of the filtration reagent is for example a post-filtration layer comprising, for example, granules of activated carbon. The thicknesses and volumes of each of the layers are, for example, calculated as a function of a necessary and / or desired residence time.

An example of implementation of a fer-sand mixture for a mercury polluted water treatment device has been studied in the laboratory and is described below.

Table 1: Characteristics of the test

Parameter Values

Iron / Sand ratio m / m

Granulometry of iron μιτι 80-140

Sand particle size mm 0-4

Load density m ³ / h / m ³ 6.0

Residence time min 10

The percentage of iron in the iron-sand mixture is 10% by weight (the unit m / m in Table 1 means mass / mass). The granulometry of the iron is between 80 μιτι and 140 μιτι and that of the siliceous sand between 0 mm and 4 mm. The volume load represents a ratio between the flow of water in m ³ / hour and the volume of filtration reagent in m ³ .

Water polluted with metallic mercury (Hg °, SUEZ CHEMICALS) and / or ionic mercury (Hg ²⁺ ) was used.

In particular, 5 L (five liters) of water to be treated were doped with mercury in the Hg ° metal and divalent ion HgC form as follows.

A few droplets of mercury were placed in the 5 L of water. The set was placed on a turntable for four (4) hours. After mixing, the mercury concentration in the water is 15 g / L.

Then, the mercury concentration was adjusted to 30 g / L by addition of HgCl 2 (addition of 80 μl of a 1 g / l solution of HgC).

Various tests have been conducted with a total mercury concentration in water of between about 10 g / L and about 400 g / L, as summarized in the table below. Table 2: Results of the test

Concentration Concentration of

\ mercury inlet mercury outlet

Abatement \

(Hg ° and / or Hg ²⁺ ) in (Hg ° and / or g ² *) in

water to treat the treated water

1 1, 0 <1 100

13.5 <1100

29.7 <1 100

30.5 <1 100

155 <1,100

176 7.6 96

198 12.8 94

361 3.1 99

389 1 1, 8 97

The mercury-polluted water is pumped using a peristaltic pump and then passes through the 10% iron-sand mixture placed in a 10 mL filter cartridge with a slenderness of 5. The mercury is dosed as input and output (eg by SAA - Atomic Absorption Spectrometry - (Hg3000 analyzer, SMT)).

The flow rate of the peristaltic pump is set at 1 mL / min.

At first, polluted water at about 30 g / L circulated through the cartridge and the water more concentrated at 400 g / L.

Water polluted at approximately 30 g / L in mercury is treated in total after passing through the mixture.

The residual concentration at the cartridge outlet is much less than 1.0 g / L. The allowance is considered 100% at this concentration.

For higher concentrations, for example of the order of

200 g / L, the maximum residual concentration measured is about 12.8 g / L. The allowance is therefore greater than 93.5%, for a residence time of only 10 minutes.

Claims

1. Device for treating mercury polluted water comprising: an enclosure (1) containing a filtration reagent (5, 6, 7), an inlet (3) for water to be treated in the enclosure (1) upstream of the reagent filter (5, 6, 7) and an outlet (4) of treated water from the enclosure (1) downstream of the filtration reagent (5, 6, 7), characterized in that the filtration reagent (5 , 6, 7) comprises a mixture (6) of iron and a chemically inert granular carrier.

2. Device according to claim 1, characterized in that a ratio N = D15 d85, with D15 corresponding to the passing diameter of the granular support at 15% by weight and d85 to the diameter passing from iron to 85% by weight, is equal to or lower at 1 1, preferably is between about 3 and about 5.

3. Device according to any one of claims 1 or 2, characterized in that the iron is in the form of shot, powder and / or chip, or any other fractional form allowing the penetration of water.

4. Device according to any one of claims 1 to 3, characterized in that the chemically inert granular carrier comprises sand and / or siliceous gravel, silica beads, glass, or even plastics.

5. Device according to any one of claims 1 to 4, characterized in that the mixture (6) comprises between about 1% and about 50% by weight of iron, preferably between about 1% and about 25% by weight, even more preferably between about 5% and about 20% by weight.

6. Device according to any one of claims 1 to 5, characterized in that the filtering reagent further comprises at least one additive.

7. Device according to claim 6, characterized in that the at least one additive comprises elemental sulfur.

8. Device according to any one of claims 6 or 7, characterized in that the at least one additive comprises at least one specific ion exchange resin.

9. Device according to any one of claims 6 to 8, characterized in that the at least one additive comprises activated carbon.

10. Device according to any one of claims 6 to 9, characterized in that the at least one additive is mixed in the mass of the iron-granular support mixture.

1 1. Device according to any one of claims 6 to 10, characterized in that the at least one additive constitutes at least one independent layer, implanted upstream and / or downstream of the mixture (6) iron-granular support.

12. Device according to any one of claims 1 to 1 1, characterized in that the filtration reagent (5, 6, 7) comprises a plurality of layers configured to be successively traversed by the water to be treated.

13. Device according to claim 12, characterized in that the filtration reagent (5, 6, 7) comprises a pre-filtration layer (5) upstream of at least the mixture (6) granular iron-support, the layer of pre-filtration (5) having a permeability at least ten times greater than that of the granular iron-carrier mixture (6) and / or an iron content of between about 20% and about 40% by weight.

14. Use of a mixture (6) comprising iron and a chemically inert granular carrier for treating mercury polluted water.

15. Method for treating mercury polluted water by a device according to any one of claims 1 to 13, comprising:

- A step of introducing a volume of water into the chamber (1) of the device by the water inlet (3) of the device;

A step of transit of the volume of water in contact with the filtration reagent (5, 6, 7), during a residence time equal to or less than two hours;

A step of precipitating the mercury, with the iron of the granular iron-support mixture (6) of the filtration reagent (5, 6, 7), comprising a mercury reduction step and a mercury microdroplet formation step; and

- A step of extracting the volume of water out of the device by the water outlet (4) of the device.